Image forming apparatus, image forming method, and data recording medium

ABSTRACT

A method of forming an image includes forming, on a recording medium (P), a special-light responsive image (201) that includes an image forming material including a special-light responsive image forming material that reacts to special light other than visible light and a special-light irresponsive image (202) that includes an image forming material including the special-light responsive image forming material. The special-light responsive image forming material of the special-light irresponsive image (202) is less than the special-light responsive image forming material of the special-light responsive image (201), and the special-light irresponsive image (202) is a prevention image that prevents visibility of the special-light responsive image (201). The forming includes forming an overlaid portion (203) in which at least a portion of one of the prevention image and the special-light responsive image (201) is overlaid on top of another one of the prevention image and the special-light responsive image (201).

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is based on and claims priority pursuant to 35U.S.C. § 119(a) to Japanese Patent Application Nos. 2020-082085 and2020-169368, filed on May 7, 2020, and Oct. 6, 2020, respectively, inthe Japan Patent Office, the entire disclosures of which are herebyincorporated by reference herein.

BACKGROUND Technical Field

Embodiments of the present disclosure relate to an image formingapparatus, an image forming method, and a data recording medium.

Background Art

In the related art, image forming apparatuses are known that can form aspecial-light responsive image including a special-light responsiveimage forming material that reacts to special light other than visiblelight and a special-light irresponsive image including the special-lightresponsive image forming material less than the special-light responsiveimage.

The above image forming apparatus is known to print a special-lightresponsive image onto a recording medium using black toner that servesas a special-light responsive image forming material and has infraredlight absorption characteristics, and print a concealing layer as abackground image of the special-light responsive image, which serves asa prevention image, using an infrared light non-absorbing material thathas the same color as that of the special-light responsive image andserves as a special-light irresponsive image forming material.

According to the related art, a special-light responsive image can beconcealed so as to be invisible by printing a concealing layer whosecolor is same as that of the special-light responsive image as abackground image of the special-light responsive image. Moreover, in therelated art, the concealing layer is printed so as not to overlap withthe special-light responsive image, the surface of a recording mediumonto which an image is to be printed are free from projections ordepressions and are smoothly flat.

SUMMARY

Embodiments of the present disclosure described herein provide threemethods of forming an image. The first method includes forming, on arecording medium, a special-light responsive image that includes animage forming material including a special-light responsive imageforming material that reacts to special light other than visible lightand a special-light irresponsive image that includes an image formingmaterial including the special-light responsive image forming material.The special-light responsive image forming material of the special-lightirresponsive image is less than the special-light responsive imageforming material of the special-light responsive image, and thespecial-light irresponsive image is a prevention image that preventsvisibility of the special-light responsive image. The forming includesforming an overlaid portion in which at least a portion of one of theprevention image and the special-light responsive image is overlaid ontop of another one of the prevention image and the special-lightresponsive image, and density of adherence of the image forming materialin the overlaid portion is smaller than density of adherence of theimage forming material in a non-overlaid portion in which one of theprevention image and the special-light responsive image is not overlaidon top of another one of the prevention image and the special-lightresponsive image. The second method of forming an image includesforming, on a recording medium, a special-light responsive image thatincludes an image forming material including a special-light responsiveimage forming material that reacts to special light other than visiblelight and a special-light irresponsive image that includes an imageforming material including the special-light responsive image formingmaterial. In the second method, the special-light responsive imageforming material of the special-light irresponsive image is less thanthe special-light responsive image forming material of the special-lightresponsive image, and the special-light irresponsive image is aprevention image that prevents visibility of the special-lightresponsive image. Moreover, in the second method, the prevention imageand the special-light responsive image are overlaid on top of each otheronly at an edge face of the prevention image or an area within aprescribed range from the edge face of the prevention image and an edgeface of the special-light responsive image or an area within aprescribed range from the edge face of the special-light responsiveimage. The third method includes forming, on a recording medium, aspecial-light responsive image that includes an image forming materialincluding a special-light responsive image forming material that reactsto special light other than visible light and a special-lightirresponsive image that includes an image forming material including thespecial-light responsive image forming material, forming a mixed imagearound the special-light responsive image, the mixed image including thespecial-light responsive image forming material less than thespecial-light responsive image forming material of the special-lightresponsive image and more than the special-light responsive imageforming material of the special-light irresponsive image, and formingthe special-light irresponsive image around the mixed image. In thethird method, the special-light responsive image forming material of thespecial-light irresponsive image is less than the special-lightresponsive image forming material of the special-light responsive image.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of embodiments and the many attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings.

FIG. 1 is a diagram illustrating a schematic configuration of a printeraccording to an embodiment of the present disclosure.

FIG. 2A is a diagram illustrating how an infrared (IR) image and ajamming image appear when these images are irradiated with infraredlight, according to an embodiment of the present disclosure.

FIG. 2B is a diagram illustrating how a jamming image appears undervisible light, according to an embodiment of the present disclosure.

FIG. 3A is a sectional view of an IR image and a jamming image when thedensity of adherence of toner of a jamming image at an overlappingregion is equivalent to the density of adherence of toner at the otherregions, according to an embodiment of the present disclosure.

FIG. 3B is a sectional view of an IR image and a jamming image when thedensity of adherence of toner of the jamming image at an overlappingregion is smaller than the density of adherence of toner at the otherregions, according to an embodiment of the present disclosure.

FIG. 4 is a graph illustrating the density of adherence of toner atvarying positions of a jamming image, according to an embodiment of thepresent disclosure.

FIG. 5 is a sectional view of an IR image and a jamming image, where thedensity of adherence of toner of both the IR image and the jamming imageis reduced at an overlapping region, according to an embodiment of thepresent disclosure.

FIG. 6 is a sectional view of an IR image and a jamming image, where anedge face of the jamming image is overlaid with the IR image, accordingto an embodiment of the present disclosure.

FIG. 7 is a diagram illustrating an image forming apparatus according toa modification of the above embodiments of the present disclosure.

FIG. 8 is a diagram illustrating an image forming apparatus according toanother modification of the above embodiments of the present disclosure.

FIG. 9 is a sectional view of the IR image and the jamming image on amixed image around an IR image where IR toner and normal color toner donot overlap with one another, according to an embodiment of the presentdisclosure.

The accompanying drawings are intended to depict embodiments of thepresent disclosure and should not be interpreted to limit the scopethereof. The accompanying drawings are not to be considered as drawn toscale unless explicitly noted.

DETAILED DESCRIPTION

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the presentdisclosure. As used herein, the singular forms “a”, “an” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise. It will be further understood that the terms“includes” and/or “including”, when used in this specification, specifythe presence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

In describing example embodiments shown in the drawings, specificterminology is employed for the sake of clarity. However, the presentdisclosure is not intended to be limited to the specific terminology soselected and it is to be understood that each specific element includesall technical equivalents that have the same structure, operate in asimilar manner, and achieve a similar result.

In the following description, illustrative embodiments will be describedwith reference to acts and symbolic representations of operations (e.g.,in the form of flowcharts) that may be implemented as program modules orfunctional processes including routines, programs, objects, components,data structures, etc., that perform particular tasks or implementparticular abstract data types and may be implemented using existinghardware at existing network elements or control nodes. Such existinghardware may include one or more central processing units (CPUs),digital signal processors (DSPs), application-specific integratedcircuits (ASICs), field-programmable gate arrays (FPGAs), computers orthe like. These terms may be collectively referred to as processors.

Unless specifically stated otherwise, or as is apparent from thediscussion, terms such as “processing” or “computing” or “calculating”or “determining” or “displaying” or the like, refer to the action andprocesses of a computer system, or similar electronic computing device,that manipulates and transforms data represented as physical, electronicquantities within the computer system's registers and memories intoother data similarly represented as physical quantities within thecomputer system memories or registers or other such information storage,transmission or display devices.

A color printer, which serves as an image forming apparatus, to which amethod according to an embodiment of the present disclosure is appliedis described below with reference to the accompanying drawings. Such acolor printer according to the present embodiment will be referred tosimply as a printer in the following description.

In the present embodiment, the apparatus according to an embodiment ofthe present disclosure is applied to an image forming apparatus withfour or less stations. The image forming apparatus according to thepresent embodiment is satisfactory as long as it can form an invisibleimage onto a recording medium using special toner that forms aninvisible image. In other words, the apparatus according to anembodiment of the present disclosure may be applied not only to aprinter but also to a copier alone, facsimile (FAX) alone, or amultifunction peripheral (MFP) that has at least two functions of aprinter, a copier, a facsimile, and a scanner.

The printer according to the present embodiment uses a special toner toform an invisible image. For example, such a special toner is used toembed additional information onto a visible image. For the purposes ofpreventing illegal copy or the like, a special toner is used when aninvisible image, for example, a textual image such as the image of“COPY” that cannot visually be recognized by human eyes, is to be formedon a recording medium together with a visible image that is formed bycolor toner. Such an invisible image may also be referred to as, forexample, invisible patterns and a ground tint. Alternatively, a specialtoner may be used when a coded image made of a visible image and a codedimage made of an invisible image are to be formed on a recording mediumin an overlapping manner for the purposes of increasing the amount ofinformation of a coded image such as a bar code image or a quickresponse (QR) code (registered trademark) image. In some embodiments, aspecial toner may be used when only an invisible image is to be formedon a recording medium and no visible image is to be formed.

As will be described later in detail, an invisible image according tothe present embodiment is formed by toner whose transparency is higherthan the transparency of normal color toner under visible light, and ismade visible as, for example, light emission and color reproduction areperformed by the irradiation with infrared light or the like.

As special toner that serves as a special-light responsive image formingmaterial, for example, infrared light absorption toner that hastransparency, and fluorescent toner that has transparency and emitsfluorescent light when irradiated with ultraviolet (UV) light are knownin the art. Such toner absorbs the light outside the optical range ofvisible light or emits light within the optical range of visible lightin response to the light outside the optical range of visible light isknown in the art. In the present embodiment, infrared light absorptiontoner is used as special toner. In the following description, referencesigns are used for some components of the apparatus according to thepresent embodiment. In particular, yellow toner, magenta toner, cyantoner, and infrared light absorption toner may be referred to as Y (Ytoner), M (M toner), C (C toner), and IR (IR toner), respectively.Moreover, it is desired that clear toner with transparency be used asspecial toner. The color reproduction of such toner is controlled undervisible light. Note also that such clear toner contains a less amount ofpigment than normal color toner that serves as special-lightirresponsive image forming material.

A special-light responsive image according to the present embodimentcontains a larger amount of infrared light absorber than a special-lightirresponsive image per each unit of dimension. In order to form aspecial-light responsive image, infrared light absorption toner (IRtoner) that forms a special-light responsive image is configured tocontain more infrared light absorber that serves as a special-lightresponsive image forming material than the color toner that forms aspecial-light irresponsive image.

In particular, preferably, the transmittance of infrared light ofinfrared light absorption toner (IR toner) that forms a special-lightresponsive image according to the present embodiment when a solid imageis to be printed is equal to or less than 40%, and the transmittance ofinfrared light of normal color toner that forms a special-lightirresponsive image is equal to or greater than 60%. Note also that bothinorganic materials and organic materials may be used as infrared lightabsorber that makes up infrared light absorption toner (IR toner).

Previously, various kinds of infrared light absorber that hastransparency and is used to achieve invisibility are under study toimplement technologies to embed additional data, and various kinds ofmaterials have been proposed. For example, inorganic materials includingrare-earth metal such as ytterbium (Yb) and infrared light absorberhaving copper phosphoric acid crystallized glass are known in the art.Moreover, organic materials including, for example, aluminum compoundand croconium pigment are known in the art, and organic materialsincluding infrared light absorber, which have the maximum wavelength forspectral absorption at 750 to 1100 nanometers (nm), have been suggested.The absorbance of such organic materials at the wavelength of 650nanometers (nm) is equal to or smaller than 5% of the absorbance at themaximum wavelength for spectral absorption. Furthermore, the usage ofnaphthalocyanine pigment has been proposed, and naphthalocyanine pigmentis advantageous in difference between the absorbance of visible lightand the absorbance of infrared light.

An infrared light absorber of inorganic materials may be, for example, aglass obtained by adding transition metal ion or a material such as apigment composed of at least one of inorganic compound and organiccompound to a known glass mesh forming material such as phosphoric acid,silica, and boric acid that transmits the light of wavelengths within avisible range, and a crystallized glass obtained by crystallizing theobtained glass with heat treatment. As such inorganic materials reflectthe light within a visible area as desired, an invisible image can beobtained.

An infrared light absorber of organic materials may be, for example,colored materials such as phthalocyanine compounds and anthraquinonecompounds and colorless materials such as aluminum salt compounds andnaphthalocyanine compounds. Among these materials, colorless materialsare preferred. This is because colorless materials do not color theimage when the colorless materials are added, and the amount ofcolorless materials to be added is relatively small as the absorbingpower for the range of infrared light is sufficiently large. In mostcases, colorless materials do not impair the image quality of the colorimage. In particular, naphthalocyanine compounds are preferred fromamong several kinds of colorless materials. This is becausenaphthalocyanine compounds have very low absorbance for the range ofvisible light and are characterized by its absolute colorlessness.Further, naphthalocyanine compounds have little influence on theelectrical charge of toner.

Secondly, the schematic configuration or operation of the printeraccording to the present embodiment is described below.

FIG. 1 is a diagram illustrating a schematic configuration of theprinter according to the present embodiment.

The printer according to the present embodiment includes, for example,an image forming unit 1, a transfer unit 2, a recording medium supplyunit 3, a fixing device 4, a recording medium ejection unit 5, acontroller 30, an image formation controller 40.

The image forming unit 1 is provided with four processing units 6Y, 6M,6C, and 6IR that serve as a set of image forming units. Theconfiguration or structure of the four processing units 6Y, 6M, 6C, and6IR is equivalent to each other except that different types of toner areused in each one of the four processing units 6Y, 6M, 6C, and 61R. Inthe present embodiment, a processing unit that uses black toner (K) isnot provided as a part of the image forming units. Accordingly, a colorimage or a monochrome image is formed using color toner of Y, M, and Conly. A processing unit that uses black toner (K) may be added as a partof the image forming units. However, such a configuration could bedisadvantageous because size of the apparatus tends to increase.

The processing unit 61R that uses IR toner may be configured in adetachable manner, or the printer according to the present embodimentmay be configured such that a processing unit that uses K toner may beinstalled instead of the processing unit that uses the IR toner. In sucha configuration, a processing unit of K toner may be mounted when animage is to be formed without using the TR toner. By so doing, a colorimage or a monochrome image can be formed using Y, M, and C color tonerand K color toner.

Alternatively, all processing units may be made removable, and thepositions at which these processing units are installed may beinterchanged with each other. In such a configuration, the positions ofthe processing unit that uses IR toner may be interchanged to switch therelative positions of the IR toner image and the multiple color tonerimage, i.e., the relative positions of the IR toner image and themultiple color toner image in the toner-image stacking direction, on arecording medium on an as-needed basis.

In the present embodiment, each one the four processing units 6Y, 6M,6C, and 61R includes, for example, a photoconductor 7 that serves as alatent-image bearer and bears a latent image, a charging roller 8 thatserves as a charger and evenly charges the surface of the photoconductor7, a developing device 9 that serves as a developing unit and develops alatent image on the surface of the photoconductor 7, and aphotoconductor cleaner 10 that serves as a latent-image bearer cleaningunit and cleans the surface of the photoconductor 7. A plurality ofexposure devices 11 that serve as latent image forming units and form alatent image on the surfaces of the photoconductors 7 are arranged atpositions facing the multiple photoconductors 7. In the presentembodiment, a light-emitting diode (LED) unit is used as the exposuredevice 11. However, no limitation is indicated thereby, and a laser-beamscanning exposure device that uses laser diodes may be adopted.

In the transfer unit 2, a seamless intermediate transfer belt 12 thatserves as an intermediate transferor and is a belt onto which the tonerimage on the photoconductor 7 is transferred, a plurality of primarytransfer rollers 13 that serve as primary transfer units and primarilytransfer the image on the photoconductor 7 onto an intermediate transferbelt 12, a secondary transfer roller 14 that serves as a secondarytransfer unit and secondarily transfers the toner image that istransferred to the intermediate transfer belt 12 to the recordingmedium, and a belt cleaner 17 that serves as an intermediate transferorcleaning unit and cleans the outer circumferential surface of theintermediate transfer belt 12 are arranged.

The intermediate transfer belt 12 is stretched by a drive roller 15 andat least one driven roller 16 and goes round as the drive roller 15rotates on the axis. The multiple primary transfer rollers 13 arearranged so as to press the intermediate transfer belt 12 against themultiple photoconductors 7. Due to such a configuration, a plurality ofprimary transfer nips at which the images on the multiplephotoconductors 7 are transferred onto the intermediate transfer belt 12are formed at a plurality of contact portions where the intermediatetransfer belt 12 contacts the multiple photoconductors 7. On the otherhand, the secondary transfer roller 14 is arranged so as to contact aportion of the intermediate transfer belt 12 that is wrapped around thedrive roller 15. Due to such a configuration, a secondary transfer nipat which the image on the intermediate transfer belt 12 is transferredonto the recording medium is formed at a contact portion where theintermediate transfer belt 12 contacts the secondary transfer roller 14through the recording medium.

In the recording medium supply unit 3, a sheet tray 18 that serves as arecording medium storage and stores a sheet of paper P as a recordingmedium, a paper feeding roller pair 19 that serves as a recording mediumfeeding unit and feeds the sheet of paper P from the sheet tray 18, atiming roller pair 20 that serves as a recording medium conveyance unitand conveys the sheets of paper P that are fed by the paper feedingroller pair 19 to the secondary transfer nip at a prescribed timing arearranged. Note also that the recording medium may be, for example, anoverhead projector (OHP) sheet, an OHP film, and a fabric in addition toa sheet of paper. In addition to plain paper, the sheet of paper may beother various kinds of sheets including, for example, a cardboard, apostcard, an envelope, thin paper, coated paper, art paper, tracingpaper, and Japan paper whose surface is uneven and not very smooth.

In the fixing device 4, a fixing device 21 that serves as a fixing unitand fixes an image onto the sheet of paper P is arranged. The fixingdevice 21 includes, for example, a fixing roller 22 that serves as afixing unit and is heated by a heat source such as a heater, and apressure roller 23 that serves as a pressurizer and is pressed againstthe fixing roller 22 with predetermined level of pressure to form afixing nip.

In the recording medium ejection unit 5, an output roller pair 24 thatserves as a recording medium ejection unit and ejects the sheet of paperP that is conveyed through the fixing device 21 to the outside of theapparatus, and an output tray 25 that serves as a recording mediumcontainer in which the sheet of paper P ejected through the outputroller pair 24 is held are arranged.

The controller 30 is in charge of the overall control of the printer,and performs image processing on the image data input from, for example,a personal computer (PC) or a reading device such as a scanner. Theimage formation controller 40 controls the image-forming operationperformed by each element of the printer such as the image forming unit1, the transfer unit 2, the recording medium supply unit 3, the fixingdevice 4, and the recording medium ejection unit 5, under control of thecontroller 30.

In addition to the above multiple elements as described above, theprinter according to the present embodiment is provided with a pluralityof toner cartridges 26 that serve as a granular material container inwhich a granular material, i.e., toner in the present embodiment, usedto form an image is stored. Each one of the multiple toner cartridges 26stores the toner of the color same as the color of the toner inside thecorresponding one of the multiple developing devices 9, and the tonercartridge 26 supplies the developing device 9 with the toner when theamount of the toner inside the corresponding one of the multipledeveloping devices 9 runs below a predetermined amount. Furthermore, theprinter according to the present embodiment is provided with awaste-toner container 27, which serves as another granular materialcontainer, in addition to the toner cartridge 26. The waste-tonercontainer 27 stores the waste toner retrieved by the belt cleaner 17 orthe photoconductor cleaner 10.

As illustrated in FIG. 1, the printer according to the presentembodiment is provided with a cover 101 used to open and close the upperside of a housing 100 of the image forming apparatus. The cover 101 ispivotable in the up-and-down directions around a rotation axis 103provided for the housing 100 of the image forming apparatus. Under thecover 101, a container holder 102 is arranged in which four tonercartridges 26 can be stored in a removable manner. The container holder102 is pivotable in the up-and-down directions around another rotationaxis 104 provided for the housing 100 of the image forming apparatus.

In the present embodiment, the processing unit 6IR that uses IR toner isarranged on the downstream side in the direction of travel of theintermediate transfer belt 12 and the processing units 6Y, 6M, and 6Cthat use color toner are arranged on the upstream side such that IRtoner image composed of IR toner, which may be referred to as aspecial-toner image, will be formed on the recording medium sidecompared with the color toner images composed of Y color toner, M colortoner, and C color toner. In other words, the Y toner image, the M tonerimage, the C toner image, and the IR toner image are stacked on top ofeach other on the intermediate transfer belt 12 in the order listed fromthe belt side. However, when the secondarily transfer is complete, theIR toner image, the C toner image, the M toner image, and the Y tonerimage are stacked on top of each other in the order listed from therecording medium side.

As described above, an IR toner image is formed on the recording mediumside compared with the color toner images. Due to such a configuration,the IR toner image is hidden by the color toner images as desired, andthe visibility of the IR toner image decreases. Moreover, theinvisibility of the image formed by IR toner can easily be secured.However, no limitation is indicated thereby, and the relative positionsof the IR processing unit 61R that uses IR toner and the processingunits 6Y, 6M, and 6C that use color toner may be adjusted as desired. Asdescribed as above, when the positions at which these processing units6Y, 6M, 6C, and 61R are installed are configured to be interchangeablewith each other, the position of the processing unit that uses IR tonercan be changed as desired.

The basic operation of the printer according to the present embodimentis described below. When an image forming operation is started, themultiple photoconductors 7 are driven to rotate, and the surfaces of thephotoconductors 7 are evenly charged to a predetermined polarity by themultiple charging rollers 8. Subsequently, the exposure devices 11irradiate the electrically-conductive surfaces of the multiplephotoconductors 7 with laser beams based on the image data input from,for example, a personal computer (PC) or a reading device such as ascanner. Accordingly, an electrostatic latent image is formed.

The latent image that is formed on each one of the photoconductors 7 isa latent image that is formed based on the single-color image dataobtained by separating a desired full-color image into a plurality ofcolor images of Y, M, and C. More specifically, the input image data isconverted and decomposed into YCM color data to generate single-colorimage data using a color conversion and decomposition table with whichthe color data of the input image, for example, red, green, and blue(RGB) or yellow, cyan, and magenta (YCM), is converted and decomposedinto color data (yellow, cyan, or magenta (YCM)) for the printeraccording to the present embodiment, and the multiple exposure devices11 that correspond to the yellow, cyan, and magenta (YCM) colors,respectively, form the latent image of each color on the correspondingone of the multiple photoconductors 7, based on the image data in YCMcolors.

In the present embodiment, the infrared (IR) image data is generatedbased on, for example, the additional information included in the inputimage data and the additional information added by the printer accordingto the present embodiment. The additional information included in theinput image data may be the information added by an applicationinstalled onto a personal computer, or may be the information added bythe printer driver installed onto a personal computer. The exposuredevice 11 for IR images forms an IR latent image, based on the TR imagedata, on one of the photoconductors 7 that corresponds to the processingunit 6IR that uses IR toner.

The multiple latent image of Y color, C color, M color, or IR that isformed on each one of the photoconductors 7 is supplied with toner fromthe corresponding one of the developing devices 9, and is developed astoner image of Y color, C color, M color, or IR. The toner images thatare formed on the multiple photoconductors 7 are sequentiallytransferred onto the rotating intermediate transfer belt 12 bysuperimposing multiple images on top of one another. More specifically,once one of the toner images on the photoconductor 7 is conveyed andreaches the position of the primary transfer nip, the toner images onthe multiple photoconductors 7 are sequentially transferred onto theintermediate transfer belt 12 by the transfer electric field formed as apredetermined level of voltage is applied the primary transfer roller13. Due to the configurations and structure as described above, afull-color toner image (visible image) composed of Y color toner, Ccolor toner, and M color toner and an IR toner image (invisible image)composed of TR toner are formed on the surface of the intermediatetransfer belt 12. Some of the toner that failed to be transferred to theintermediate transfer belt 12 and remains on each one of thephotoconductors 7 is removed by the corresponding one of thephotoconductor cleaners 10.

Once the image-forming operation starts, the paper feeding roller 19starts rotating, and the sheet of paper P is fed from the sheet tray 18.The timing roller pair temporarily halts the sheet P fed through thepaper feeding roller pair 19. Thereafter, the timing roller pair 20starts rotating at a prescribed timing and starts conveying the sheet ofpaper P to the secondary transfer nip at a timing when the full colortoner image formed on the intermediate transfer belt 12 reaches thesecondary transfer nip.

When the sheet of paper P is transferred onto the secondary transfernip, a predetermined level of voltage is applied the secondary transferroller 14. Accordingly, a transfer electric field is formed at thesecondary transfer nip, and the toner image on the intermediate transferbelt 12 is transferred onto the sheet P all at once due to the electricfield formed at the secondary transfer nip. In so doing, the residualtoner that is left on the intermediate transfer belt 12 is removed bythe belt cleaner 17.

The sheet of paper P is then conveyed to the fixing device 21, and thetoner image is fixed to the sheet of paper P as heated and pressurizedby the fixing roller 22 and the pressure roller 23. Then, the sheet ofpaper P is ejected to the outside of the apparatus by the output rollerpair 24, and is placed on the output tray 25.

The above description relates to an image forming operation when afull-color image is formed on a recording medium. However, no limitationis indicated thereby, and an image may be formed using any one of thefour processing units 6Y, 6M, 6C, and 61R. Alternatively, an image maybe formed using two or three of the four processing units 6Y, 6M, 6C,and 61R.

An IR image is not completely colorless but is in pale yellow undervisible radiation. For this reason, if the IR image exists on arecording medium on its own, there is some concern that such an IR imagecould visually be recognized under visible light, and the invisibilityof the IR image may not sufficiently be secured.

FIG. 2A is a diagram illustrating an IR image and a jamming imageirradiated with infrared light, according to the present embodiment.

FIG. 2B is a diagram illustrating a state of a jamming image undervisible light, according to the present embodiment.

In order to handle such a situation, in the present embodiment asillustrated in FIG. 2A and FIG. 2B, a jamming image 202 that serves as aprevention image and prevents the viewability of an IR image 201 undervisible light can be formed around the IR image 201 on a recordingmedium.

More specifically, whether or not the jamming image 202 is to be formedcan be selected through the operation of, for example, the control panelprovided for the apparatus and a personal computer (PC) installed with aprinter driver. When it is determined that the jamming image 202 is beformed, the controller 30 controls the image formation controller 40 toform the jamming image 202 around the IR image 201 in an automaticmanner. The area of the jamming image 202 may manually be set throughthe operation of the PC installed with printer driver software. Forexample, the IR image 201 that is formed on the recording medium, e.g.,“2018.1.1. code: 12345” as illustrated in FIG. 2A, is displayed whenmanual setting is chosen through the operation of the printer driversoftware of the PC, and the forming area of the jamming image 202 maymanually be specified.

The jamming image 202 is generated such that its color will be the sameas the color of the IR image 201 under visible light, using at least oneof the Y color toner, the C color toner, and the M color toner. Morespecifically, the jamming image 202 is formed such that the differencein gloss value between the IR image 201 and the jamming image 202 willbe equal to or smaller than 10% and the color difference ΔE between theIR image 201 and that the jamming image 202 will be equal to or smallerthan 6.5. Due to such a configuration, as illustrated in FIG. 2B, the IRimage 201 is blended into the jamming image 202, and the IR image 201cannot visually be recognized easily under visible light. When thejamming image 202 is to be formed using only a single color toner, it isdesired that the toner of Y color be used. This is because the IR image201 cannot visually be recognized easily when the image is formed by Ycolor that is most inconspicuous on a sheet of paper. By contrast, whenthe jamming image is irradiated with infrared light, the IR image emitslight and reproduces color. As a result, as illustrated in FIG. 2A, theIR image can visually be recognized easily.

In the present embodiment, the color difference ΔE can be obtained asfollows. The condition of 2-degree viewing field of the CIE StandardIlluminant D50 that serves as a light source is adopted, and the colorof each one of the IR image 201 and the jamming image 202 is measuredusing a spectrophotometric colorimeter (X-Rite eXact-scan). As a result,the value of the color difference ΔE can be calculated and obtainedbased on the multiple measured values. Note also that the colordifference ΔE is calculated based on the definition described inJapanese Industrial Standards (JIS) Z 8105 2073.

The above gloss value is measured and obtained using a glossmeter PG-1,which is produced by Nippon Denshoku Industries, Co. Ltd., at theglancing angle of 60 degrees, according to a method of measuring thegloss value of a specular surface defined in Japanese IndustrialStandards (JIS) Z8741.

FIG. 3A is a sectional view of the IR image 201 and the jamming image202 when the density of adherence of toner of the jamming image at anoverlapping region 203 is equivalent to the density of adherence oftoner at the other regions, according to the present embodiment.

FIG. 3B is a sectional view of the IR image 201 and the jamming image202 when the density of adherence of toner of the jamming image 202 atthe overlapping region 203 is smaller than the density of adherence oftoner at the other regions, according to the present embodiment.

There is some concern that the jamming image 202 may be displaced fromthe IR image 201 due to, for example, the decentering of the multiplephotoconductors. When such decentering occurs, a bare region may appearin which no toner adheres between the IR image 201 and the jamming image202. Under such conditions, there is some concern that an edge face ofthe IR image 201 may visually be recognized under visible light due tothe color difference between the IR image 201 and the white surface ofthe recording medium at such a bare region. In such cases, theinvisibility of the IR image 201 is impaired.

In order to handle such a situation, in the present embodiment, asillustrated in FIG. 3A and FIG. 3B, the jamming image 202 is formed suchthat the jamming image 202 will overlap with an edge face of the IRimage 201. Due to such a configuration, even if the jamming image 202 isslightly displaced from the IR image 201, a bare region between the IRimage 201 and the jamming image 202 can be prevented. Moreover, an edgeface of the IR image 201 can be prevented from being visually recognizedunder visible light, and the invisibility of the IR image 201 undervisible light can be secured as desired.

In the present embodiment, the width L of the overlapping region 203 inwhich the IR image 201 is overlaid with the jamming image 202 is between50 to 100 μm. However, no limitation is intended thereby, and the widthL of the overlapping region 203 may be equal to or wider than 100 μm.Alternatively, the jamming image 202 may be formed so as to cover theentirety of the IR image 201.

However, as illustrated in FIG. 3A, the overlapping region 203 in whichan edge face of the IR image 201 is overlaid with the jamming image 202tends to swell by about T1 micrometers (μm) compared with the otherportions of the image. As a result, for example, the visible light maybe reflected differently between the above overlapping region 203 andits surrounding image area. For this reason, there is some concern thatthe unevenness at the overlapping region 203 in comparison to thesurrounding area is visually recognized, and the IR image 201 isvisually recognized due to such unevenness.

In order to handle such a situation, in the present embodiment, asillustrated in FIG. 3B, the density of adherence of toner of the jammingimage 202 at the overlapping region 203 with the IR image 201 is madesmaller than the density of adherence of toner at the other regions. Dueto such a configuration, the swelling portion at the overlapping region203 in which an edge face of the IR image 201 is overlaid with thejamming image 202 can be as small as T2 micrometers (μm), and theswelling portion of the overlapping region 203 can be reduced. Note thatT2 is smaller than T1, and for example, T2 is equal to or smaller than10 μm. Due to such a configuration, the unevenness at the overlappingregion 203 in which an edge face of the IR image 201 is overlaid withthe jamming image 202 in comparison to the surrounding area can beprevented from being visually recognized under visible light, and theinvisibility of the IR image 201 can be secured as desired.

FIG. 4 is a graph illustrating the density of adherence of toner atvarying positions of the jamming image 202, according to the presentembodiment.

The density of adherence of toner indicates the density of the tonerthat is adhered per each unit of dimension, and the measurement unit ofmg/cm² is adopted in the present embodiment. Note also that the densityof adherence of toner may also be regarded as the amount of adheredtoner or the mass of the adhered toner per each unit of dimension. Inthe present disclosure, the density of toner is indicated in which thetoner is so thin that the bare region to which no toner adheres can beseen through. For example, the number of layers of stacked toner is oneor less.

The density of adherence of toner can be obtained as follows. Firstly, amagnified image with the power of two-hundred times is obtained using anoptical electron microscope, and the magnified image is binarized. Then,the ratio of the number of pixels of the toner-adhered region to thenumber of all the pixels is calculated based on the magnified andbinarized image.

As illustrated in FIG. 4, in the embodiments of the present disclosure,the density of adherence of toner of the jamming image 202 at anoverlapping region 203 is gradually reduced toward an edge face of theprevention image 202. In the present embodiment, the density ofadherence of toner of the jamming image 202 starts to be reduced from aposition B as illustrated in FIG. 4, which is slightly outside and awayfrom the overlapping region 203. As described above, the swellingportion at an edge face A of the TR image 201, i.e., the boundary regionbetween the overlapping region 203 and the jamming image 202, can bereduced due to such a configuration in which the density of adherence oftoner of the jamming image 202 starts to be reduced from a positionslightly outside and away from the overlapping region 203, and theunevenness at an edge face of the IR image 201 can be made inconspicuousand less outstanding under visible light.

As the exposure value of the multiple exposure devices 11 is graduallyreduced from the position B as illustrated in FIG. 4, which is slightlyoutside and away from the overlapping region 203, the density ofadherence of toner can gradually be reduced from the position B towardan edge face of the jamming image 202.

Alternatively, the conditions for primary transfer may be changed tocause dust particles intentionally. By so doing, the density ofadherence of toner on the jamming image 202 can gradually be reducedfrom the position B toward an edge face of the jamming image 202.

Further, a known error-diffusion method such as dithering may beadopted, and the printing rate is gradually be reduced by imageprocessing from the position B toward an edge face of the jamming image202. By so doing, the density of adherence of toner on the jamming image202 can gradually be reduced from the position B toward an edge face ofthe jamming image 202.

Alternatively, the exposure value may gradually be reduced, and theamount of adhered toner is gradually reduced. When such a method isadopted to reduce the density of adherence of toner on the jamming image202 in a gradual manner, there is some concern that the relation betweenthe amount of adhered toner and the exposure value changes depending on,for example, the environment. Further, there is some concern that thedensity of adherence of toner at the overlapping region 203 cannot bechanged to a desired density of adherence in a stable manner. In orderto stabilize the density of adherence of toner, the image-formingcondition needs to be adjusted as follows. A sensor that senses theamount of adhered toner is arranged to form a test image of toner atprescribed time intervals, and the amount of toner adhered to the formedtest image is detected by the sensor that senses the amount of adheredtoner. By so doing, the image-forming condition can be adjusted asdesired.

When the above conditions for primary transfer are adopted in which thedensity of adherence of toner at the overlapping region 203 is reducedby causing dust particles intentionally, the dust particles that arecaused by transferring process tend to affect the other images that areformed by toner whose color is same as the color of the toner used toform the jamming image 202. Further, the conditions of dust particle maydiffer due to, for example, the environment, and there is some concernthat the density of adherence of toner at the overlapping region 203cannot be changed to a desired density of adherence in a stable manner.

By contrast, the above method in which the density of adherence of toneron the jamming image 202 is gradually reduced by image processing fromthe position B toward an edge face of the jamming image 202 is desirablebecause the density of adherence of toner can be reduced to a desireddensity of adherence in a stable manner compared with cases in which thedensity of adherence of toner is reduced by manipulating the exposurevalue or the image-forming conditions such as the conditions for primarytransfer.

FIG. 5 is a sectional view of the TR image 201 and the jamming image202, where the density of adherence of toner of both the IR image 201and the jamming image 202 is reduced at the overlapping region 203,according to the present embodiment.

The density of adherence of toner of the IR image 201 at the overlappingregion 203 in which the IR image 201 is overlaid with the jamming image202 around its edge face may be reduced within a range in which the IRimage 201 is not affected in any way. Alternatively, as illustrated inFIG. 5, the density of adherence of toner of both the 1R image 201 andthe jamming image 202 may be reduced at the overlapping region 203. Dueto such a configuration, the swelling portion of the overlapping region203 can virtually be eliminated, and the invisibility of the IR image201 under visible light can further be improved.

FIG. 6 is a sectional view of the 1R image 201 and the jamming image202, where the IR image 201 overlaps with an edge face of the jammingimage 202, according to the present embodiment.

As illustrated in FIG. 6, an edge face of the jamming image 202 may beoverlaid with the IR image 201. When the processing unit 6IR that usesIR toner is arranged on the more downstream side than the processingunit 6Y, 6M, and 6C in the direction where the surface of theintermediate transfer belt 12 travels, as illustrated in FIG. 6, an edgeface of the jamming image 202 may be overlaid with the IR image 201.

Each kind of image as illustrated in FIG. 5 and FIG. 6 may be defined asfollows depending on the amount of IR toner. The IR image 201 may bedefined as an image with a relatively large amount of IR toner, and thejamming image 202 may be defined as an image with a relatively smallamount of IR toner. The above overlapping region 203 may be defined as amixed image with a not very small and not very large amount of IR toner.In other words, the overlapping region 203 contains both IR toner andcolor toner in a mixed manner.

FIG. 9 is a sectional view of the IR image 201 and the jamming image 202on a mixed image around the IR image 201 where IR toner and normal colortoner do not overlap with one another, according to the presentembodiment.

As illustrated in FIG. 9, it is not always necessary for IR toner andcolor toner to overlap with one another on a mixed image, whichcorresponds to the overlapping region in the above embodiment.

Alternatively, the jamming image 202 may be formed so as to cover theentirety of the IR image 201. In the present embodiment, the density ofadherence of toner of the jamming image 202 at an overlapping region 203with the IR image 201 is reduced. Due to such a configuration, theincrement of the amount of toner adhered to the overlapping region canefficiently be controlled. When a method is adopted in which theprinting rate at an overlapping region is reduced by image processingand the density of adherence of toner is reduced, the increment of theimage density at an overlapping region is also controlled. Due to such aconfiguration, even if the jamming image 202 is formed so as to coverthe entirety of the IR image 201, it is not likely that a fixationfailure occurs or the image density at a portion of the IR imageincreases

For this reason, the jamming image 202 may be formed so as to cover theentirety of the IR image 201.

In the above-described embodiment of the present disclosure, the IRimage 201 is formed using clear or transparent IR toner. However, nolimitation is indicated thereby, and the IR image may be formed usingcolored IR toner that is visually be recognized easily under visiblelight. For example, K toner that contains carbon black that serves as aninfrared light absorber may be used as colored IR toner. In such aconfiguration, the IR image 201 is in black, and a black jamming image202 is formed using Y color toner, M color toner, and C color toner thatdo not contain any infrared light absorber such as carbon.Alternatively, a coloring material may be added to the above clear ortransparent IR toner, and the above clear or transparent IR toner may beused as colored IR toner.

The jamming image 202 whose color is same as the color of the IR imageis formed around the colored IR image 201 that is composed of colored IRtoner. As a result, the IR image 201 is blended into the jamming image202, and the IR image 201 cannot visually be recognized easily.

FIG. 7 is a diagram illustrating an image forming apparatus according toa modification of the above embodiments of the present disclosure.

The image forming apparatus according to a modification of the aboveembodiments of the present disclosure as illustrated in FIG. 7 isprovided with a processing unit 6T that forms an image using clear tonerthat serves as a special-light irresponsive image forming material andnever absorbs infrared light or reproduces color when irradiated withinfrared light. The processing unit 6T is arranged on the moredownstream side than the processing unit 61R in the direction where thesurface of the intermediate transfer belt 12 travels.

Due to such a configuration, clear toner may be used to form the jammingimage 202, and the difference in gloss value between the IR image 201and the jamming image 202 under visible light can further be reduced. Asa result, the degree of invisibility of the IR image 201 under visiblelight can further be increased.

In particular, there is some concern that the difference in gloss valuebetween the IR image 201 and the jamming image 202 cannot be reduced to10% or less simply by Y color toner, M color toner, and C color tonerwhen the color tone of the IR toner is low under visible light and theamount of non-IR toner to reproduce the color tone tends to be verysmall in the first place. When IR toner with low color tone is to beused, it is desired that a processing unit 6T be provided and that thejamming image be formed using clear toner and at least one of Y colortoner, M color toner, and C color toner. By so doing, the difference ingloss value between the IR image 201 and the jamming image 202 can bereduced to a value equal to or smaller than 10%, and the color of thejamming image 202 can be made the same as the color of the TR image 201.

FIG. 8 is a diagram illustrating an image forming apparatus according toanother modification of the above embodiments of the present disclosure.

The image forming apparatus according to another modification of theabove embodiments of the present disclosure as illustrated in FIG. 8includes a full-color image forming apparatus 200 and an IR imageforming apparatus 300 that forms an IR image.

The IR image forming apparatus 300 includes an IR processing unit 306IRthat is optionally installed in the full-color image forming apparatus200 to form the IR image 201 using IR toner, and a jamming processingunit 306J that forms the jamming image 202 using jamming toner thatserves as special-light irresponsive image forming material. The colorof such jamming toner is same as the color of the IR toner under visiblelight, and such jamming toner never absorbs infrared light or reproducescolor when irradiated with infrared light. Moreover, the jamming toneraccording to the present embodiment is adjusted such that its color willbe same as the color of the IR toner under visible light, using cleartoner and at least one of Y color toner, M color toner, C color toner,and K color toner.

In the present embodiment, the sheet of paper P on which an image isformed by the full color image forming apparatus 200 is conveyed to theIR image forming apparatus 300. Then, an IR toner image is formed at apredetermined position of the sheet of paper P, and a jamming tonerimage is formed around the IR image. Then, the IR toner image and thejamming toner image are fixed onto the sheet of paper P by the fixingdevice 304, and the sheet of paper P is ejected to the output tray 301.

In the image forming apparatus as illustrated in FIG. 1 or FIG. 7, thefixing condition needs to be determined such that the images other thanthe jamming image and the IR image will be formed as desired. However,in the present modification of the above embodiments as illustrated inFIG. 8, the fixing condition of the fixing device 304 can be determinedwithout regard for the images other than the jamming image and the IRimage. For this reason, for example, the fixing condition of the fixingdevice 304 can optimally be determined such that there will be nodifference in gloss value between the jamming image 202 and the IR image201. Moreover, in the configuration as illustrated in FIG. 8, thetransfer condition in which dust particles are caused by transferringprocess may be selected when a jamming toner image is to be transferredto a sheet of paper. Even if such a transfer condition is selected, theother images are not affected. When an IR image is to be formed in theconfiguration as illustrated in FIG. 1 and FIG. 7, the processing unit6K that uses K color toner needs to be replaced with the processing unit6IR that uses IR toner. However, such replacement is no longer necessaryin the configuration as illustrated in FIG. 8 and saving in time can beachieved.

The embodiments described above are given as an example, and uniqueadvantageous effects are achieved for each of the first to sixteenthmodes given below.

First Mode

An image forming apparatus forms, on a recording medium, a special-lightresponsive image such as the IR image 201 including an image formingmaterial including a special-light responsive image forming materialsuch as IR toner that reacts to special light such as infrared lightother than visible light and a special-light irresponsive imageincluding the special-light responsive image forming material. Forexample, the special-light irresponsive image is composed of Y, M, and Ctoner. In the image forming apparatus according to the first mode of thepresent disclosure, the special-light responsive image forming materialof the special-light irresponsive image is less than the special-lightresponsive image forming material of the special-light responsive image.In the first mode of the present disclosure as described above, thespecial-light irresponsive image is used as a prevention image such asthe jamming image 202 that prevents visibility of the special-lightresponsive image, and at least a portion of one of the special-lightirresponsive image and the special-light responsive image is overlaid ontop of another one of the special-light irresponsive image and thespecial-light responsive image. Moreover, the density of adherence ofthe image forming material over the portion where at least one of theprevention image and the special-light responsive image is overlaid ontop of the other one of the prevention image and the special-lightresponsive image is smaller than the density of adherence of the imageforming material at a portion where the one of the prevention image andthe special-light responsive image is not overlaid on top of the otherone of the prevention image and the special-light responsive image.

As a prevention image such as the jamming image 202 is formed so as tobe overlaid on top of a special-light responsive image such as the IRimage 201, the appearance of a bare region between the special-lightresponsive image and the prevention image can be prevented even if theprevention image is slightly displaced from the special-light responsiveimage when the prevention image is formed over the special-lightresponsive image. Due to such a configuration according to the firstmode of the present disclosure, the special-light responsive image canbe blended into the prevention image as desired under visible light, andthe visibility of the special-light responsive image can be prevented asdesired.

Moreover, in the first mode of the present disclosure as describedabove, the density of adherence of the image forming material such astoner at the overlapping region 203 where the at least one of theprevention image and the special-light responsive image is overlaid withthe other one of the prevention image and the special-light responsiveimage is made smaller than the density of adherence of the image formingmaterial such as toner at the overlapping region 203 where the at leastone of the prevention image and the special-light responsive image isnot overlaid with the other one of the prevention image and thespecial-light responsive image. Due to such a configuration according tothe first mode of the present disclosure, compared with theconfiguration in which the density of adherence of the image formingmaterial such as toner at the overlapping region 203 where the at leastone of the prevention image and the special-light responsive image isoverlaid with the other one of the prevention image and thespecial-light responsive image is same as the density of adherence ofthe image forming material such as toner at the overlapping region 203where the at least one of the prevention image and the special-lightresponsive image is not overlaid with the other one of the preventionimage and the special-light responsive image, the swelling portion ofthe overlapping region of the two images can be reduced. As a result,the visual recognition of a special-light responsive image under visiblelight due to the unevenness caused by the swelling portion of theoverlapping region of the two images can be prevented.

Second Mode

In the image forming apparatus according to the first mode of thepresent disclosure, the swelling level of the overlapping region of thetwo images with reference to the non-overlapping region is equal to orless than 10 μm.

Due to such a configuration, as described above in the embodiment of thepresent disclosure, the unevenness at the overlapping region 203 betweena special-light responsive image such as the IR image 201 and aprevention image such as the jamming image 202 in comparison to thesurrounding area can be prevented from being visually recognized undervisible light, and the invisibility of the special-light responsiveimage can be secured as desired.

Third Mode

In the image forming apparatus according to the first or second mode ofthe present disclosure, the area in which the density of adherence issmall is broader than the area of the portion in which the at least oneof the prevention image and the special-light responsive image isoverlaid with the other one of the special-light irresponsive image andthe special-light responsive image.

Due to such a configuration, as described above with reference to FIG.4, the swelling portion at the boundary region between the overlappingregion 203 and a prevention image such as the jamming image 202 can bereduced, and the unevenness at an edge face of a special-lightresponsive image such as the IR image 201 can be made inconspicuous andless outstanding under visible light.

Fourth Mode

In the image forming apparatus according to any one of the first tothird modes of the present disclosure, the density of adherence of theimage forming material over the portion where the at least one of thespecial-light irresponsive image and the special-light responsive imageis overlaid on top of the other one of the special-light irresponsiveimage and the special-light responsive image is gradually reduced towardan edge face of the one of the special-light irresponsive image and thespecial-light responsive image.

Due to such a configuration according to the fourth mode of the presentdisclosure, the unevenness at the overlapping region 203 between aspecial-light responsive image such as the IR image 201 and a preventionimage such as the jamming image 202 in comparison to the surroundingarea can be prevented from being visually recognized under visiblelight, and the invisibility of the special-light responsive image can besecured as desired.

Fifth Mode

In the image forming apparatus according to any one of the first tofourth modes of the present disclosure, the printing rate at theoverlapping region 203 where at least one of the special-lightresponsive image such as the IR image 201 and the prevention image suchas the jamming image 202 is overlaid with the other one of theprevention image and the special-light responsive image is made smallerthan the printing rate at an region where the at least one of thespecial-light responsive image such as the IR image 201 and theprevention image such as the jamming image 202 is not overlaid with theother one of the prevention image and the special-light responsiveimage.

Due to such a configuration according to the fifth mode of the presentdisclosure, as described above in the embodiment of the presentdisclosure, the density of adherence of, for example, the density ofadherence of toner at the overlapping region 203 can be reduced.Alternatively, the density of adherence may be reduced by imageprocessing. By so doing, the density of adherence of toner at theoverlapping region 203 may be reduced to a desired density of adherencein a stable manner.

Sixth Mode

In the image forming apparatus according to any one of the first tofifth modes of the present disclosure, the density of adherence of boththe special-light responsive image such as the IR image 201 and theprevention image such as the jamming image 202 is reduced over theoverlapping region.

Due to such a configuration according to the sixth mode of the presentdisclosure, as described above with reference to FIG. 5, the swellingportion of the overlapping region 203 can further be reduced, and thevisual recognition of a special-light responsive image such as an IRimage due to the swelling portion of the overlapping region 203 canfurther be prevented.

Seventh Mode

In the image forming apparatus according to any one of the first tosixth modes of the present disclosure, a prevention image and aspecial-light responsive image are formed such that these two kinds ofimages will be overlaid on top of each other only at an edge face of aprevention image such as the jamming image 202 or an area within aprescribed range from the edge face of the prevention image and an edgeface of a special-light responsive image such as the IR image 201 or anarea within a prescribed range from the edge face of the special-lightresponsive image. Due to such a configuration according to the seventhmode of the present disclosure, the consumption of toner can be reduced,and the appearance of a bare region between the special-light responsiveimage and the prevention image can be prevented.

Eighth Mode

In the image forming apparatus according to the seventh mode of thepresent disclosure, the density of adherence of an overlapping region inwhich a special-light responsive image such as the IR image 201 and aprevention image such as the jamming image 202 overlaid on top of eachother is gradually reduced toward an edge face of the special-lightresponsive image, and the density of adherence of the overlapping regionin which the special-light responsive image sand the prevention imageoverlaid on top of each other is gradually reduced toward an edge faceof the prevention image.

Due to such a configuration according to the eighth mode of the presentdisclosure, as described above with reference to FIG. 5 and FIG. 6, theswelling portion of the overlapping region 203 can further be reduced,and the visual recognition of a special-light responsive image such asan IR image due to the swelling portion of the overlapping region 203can further be prevented.

Ninth Mode

An image forming apparatus forms, on a recording medium, a special-lightresponsive image such as the IR image 201 including an image formingmaterial including a special-light responsive image forming materialsuch as IR toner that reacts to special light such as infrared lightother than visible light and a special-light irresponsive imageincluding the special-light responsive image forming material. Forexample, the special-light irresponsive image is composed of Y, M, and Ctoner. In the image forming apparatus according to the ninth mode of thepresent disclosure, the special-light responsive image forming materialof the special-light irresponsive image is less than the special-lightresponsive image forming material of the special-light responsive image.According to the ninth mode of the present disclosure, the special-lightirresponsive image is used as a prevention image such as the jammingimage 202 that prevents visibility of the special-light responsiveimage, and the prevention image and the special-light responsive imageare formed such that these two kinds of images will be overlaid on topof each other only at an edge face of the prevention image or an areawithin a prescribed range from the edge face of the prevention image andan edge face of a special-light responsive image or an area within aprescribed range from the edge face of the special-light responsiveimage.

Due to such a configuration according to the ninth mode of the presentdisclosure, the consumption of toner can be reduced, and the appearanceof a bare region between the special-light responsive image and theprevention image can be prevented.

Tenth Mode

In the image forming apparatus according to any one of the first toninth modes of the present disclosure, the color difference ΔE between aspecial-light responsive image such as the IR image 201 and a preventionimage such as the jamming image 202 under visible light is equal to orsmaller than 6.5.

Due to such a configuration according to the tenth mode of the presentdisclosure, as described above in the embodiment of the presentdisclosure, the color of a prevention image such as the jamming image202 can be made substantially the same as the color of a special-lightresponsive image such as an IR image under visible light. Accordingly,the visibility of the special-light responsive image under visible lightcan be prevented as desired by the jamming image 202.

Eleventh Mode

In the image forming apparatus according to any one of the first totenth modes of the present disclosure, the difference in gloss valuebetween a special-light responsive image such as the IR image 201 and aprevention image such as the jamming image 202 is equal to or smallerthan 10%. Due to such a configuration according to the eleventh mode ofthe present disclosure, as described above in the embodiment of thepresent disclosure, the visual recognition of the IR image 201 undervisible light due to the difference in gloss value between aspecial-light responsive image such as the IR image 201 and a preventionimage such as the jamming image 202 can be prevented.

Twelfth Mode

In the image forming apparatus according to any one of the first toeleventh modes of the present disclosure, the special light is infraredlight.

Due to such a configuration according to the twelfth mode of the presentdisclosure, a special-light responsive image such as an IR image can beread and obtained by performing irradiation with infrared light.

Thirteenth Mode

A method of forming an image, the method comprising: forming, on arecording medium, a special-light responsive image such as the IR image201 including an image forming material including a special-lightresponsive image forming material such as IR toner that reacts tospecial light such as infrared light other than visible light and aspecial-light irresponsive image including the special-light responsiveimage forming material. For example, the special-light irresponsiveimage is composed of Y, M, and C toner. In the method according to thethirteenth mode of the present disclosure, the special-light responsiveimage forming material of the special-light irresponsive image is lessthan the special-light responsive image forming material of thespecial-light responsive image. In the method according to thethirteenth mode of the present disclosure, the special-lightirresponsive image is used as a prevention image such as the jammingimage 202 that prevents visibility of the special-light responsiveimage, and at least a portion of one of the special-light irresponsiveimage and the special-light responsive image is overlaid on top ofanother one of the special-light irresponsive image and thespecial-light responsive image. Moreover, in the method according to thethirteenth mode of the present disclosure, the density of adherence ofthe image forming material over the portion of the one of thespecial-light irresponsive image and the special-light responsive imageis smaller than density of adherence of the image forming material ofthe one of the special-light irresponsive image and the special-lightresponsive image at which the special-light irresponsive image and thespecial-light responsive image are not overlaid on top of one another.

Due to such a configuration according to the thirteenth mode of thepresent disclosure, an advantageous effect similar to the advantageouseffect of the above first mode of the present disclosure can beachieved.

Fourteenth Mode

A method of forming an image, the method comprising: forming, on arecording medium, a special-light responsive image such as the IR image201 including an image forming material including a special-lightresponsive image forming material such as IR toner that reacts tospecial light such as infrared light other than visible light and aspecial-light irresponsive image including the special-light responsiveimage forming material. For example, the special-light irresponsiveimage is composed of Y, M, and C toner. In the method according to thefourteenth mode of the present disclosure, the special-light responsiveimage forming material of the special-light irresponsive image is lessthan the special-light responsive image forming material of thespecial-light responsive image. According to the fourteenth mode of thepresent disclosure, the special-light irresponsive image is used as aprevention image such as the jamming image 202 that prevents visibilityof the special-light responsive image, and the prevention image and thespecial-light responsive image are formed such that these two kinds ofimages will be overlaid on top of each other only at an edge face of theprevention image or an area within a prescribed range from the edge faceof the prevention image and an edge face of a special-light responsiveimage or an area within a prescribed range from the edge face of thespecial-light responsive image.

Due to such a configuration according to the fourteenth mode of thepresent disclosure, an advantageous effect similar to the advantageouseffect of the above ninth mode of the present disclosure can beachieved.

Fifteenth Mode

A method of forming an image, the method comprising: forming, on arecording medium, a special-light responsive image such as the IR image201 including an image forming material including a special-lightresponsive image forming material such as IR toner that reacts tospecial light such as infrared light other than visible light and aspecial-light irresponsive image including the special-light responsiveimage forming material. For example, the special-light irresponsiveimage is composed of Y, M, and C toner. In the method according to thefifteenth mode of the present disclosure, the special-light responsiveimage forming material of the special-light irresponsive image is lessthan the special-light responsive image forming material of thespecial-light responsive image. Moreover, the method according to thefifteenth mode of the present disclosure comprises:

-   forming a mixed image around the special-light responsive image, the    mixed image including the special-light responsive image forming    material less than the special-light responsive image forming    material of the special-light responsive image and more than the    special-light responsive image forming material of the special-light    irresponsive image; and-   forming the special-light irresponsive image around the mixed image.

Due to such a configuration according to the fifteenth mode of thepresent disclosure, an advantageous effect similar to the advantageouseffect of the above first mode of the present disclosure can beachieved.

Sixteenth Mode

A data recording medium such as the sheet of paper P on which an imageis to be formed, the data recording medium comprising at least one of acharacter, a sign, a code, and an image formed by the method accordingto any one of the thirteenth mode to the fifteenth mode.

Due to such a configuration according to the sixteenth mode of thepresent disclosure, a data recording medium on which the visibility ofthe special-light responsive image is prevented as desired can beprovided.

Note that numerous additional modifications and variations are possiblein light of the above teachings. It is therefore to be understood thatwithin the scope of the appended claims, the disclosure of the presentdisclosure may be practiced otherwise than as specifically describedherein. For example, elements and/or features of different illustrativeembodiments may be combined with each other and/or substituted for eachother within the scope of this disclosure and appended claims.

Further, as described above, any one of the above-described and othermethods of the present disclosure may be embodied in the form of acomputer program stored on any kind of storage medium. Examples ofstorage media include, but are not limited to, flexible disks, harddisks, optical discs, magneto-optical discs, magnetic tape, nonvolatilememory cards, read only memory (ROM), etc. Alternatively, any one of theabove-described and other methods of the present disclosure may beimplemented by ASICs, prepared by interconnecting an appropriate networkof conventional component circuits, or by a combination thereof with oneor more conventional general-purpose microprocessors and/or signalprocessors programmed accordingly.

What is claimed is:
 1. A method of forming an image, the methodcomprising forming, on a recording medium, a special-light responsiveimage that includes an image forming material including a special-lightresponsive image forming material that reacts to special light otherthan visible light and a special-light irresponsive image that includesan image forming material including the special-light responsive imageforming material, wherein the special-light responsive image formingmaterial of the special-light irresponsive image is less than thespecial-light responsive image forming material of the special-lightresponsive image, wherein the special-light irresponsive image is aprevention image that prevents visibility of the special-lightresponsive image, wherein the forming includes forming an overlaidportion in which at least a portion of one of the prevention image andthe special-light responsive image is overlaid on top of another one ofthe prevention image and the special-light responsive image, and whereindensity of adherence of the image forming material in the overlaidportion is smaller than density of adherence of the image formingmaterial in a non-overlaid portion in which one of the prevention imageand the special-light responsive image is not overlaid on top of anotherone of the prevention image and the special-light responsive image.
 2. Amethod of forming an image, the method comprising forming, on arecording medium, a special-light responsive image that includes animage forming material including a special-light responsive imageforming material that reacts to special light other than visible lightand a special-light irresponsive image that includes an image formingmaterial including the special-light responsive image forming material,wherein the special-light responsive image forming material of thespecial-light irresponsive image is less than the special-lightresponsive image forming material of the special-light responsive image,wherein the special-light irresponsive image is a prevention image thatprevents visibility of the special-light responsive image, and whereinthe prevention image and the special-light responsive image are overlaidon top of each other only at an edge face of the prevention image or anarea within a prescribed range from the edge face of the preventionimage and an edge face of the special-light responsive image or an areawithin a prescribed range from the edge face of the special-lightresponsive image.
 3. A method of forming an image, the methodcomprising: forming, on a recording medium, a special-light responsiveimage that includes an image forming material including a special-lightresponsive image forming material that reacts to special light otherthan visible light and a special-light irresponsive image that includesan image forming material including the special-light responsive imageforming material; forming a mixed image around the special-lightresponsive image, the mixed image including the special-light responsiveimage forming material less than the special-light responsive imageforming material of the special-light responsive image and more than thespecial-light responsive image forming material of the special-lightirresponsive image; and forming the special-light irresponsive imagearound the mixed image, wherein the special-light responsive imageforming material of the special-light irresponsive image is less thanthe special-light responsive image forming material of the special-lightresponsive image.
 4. A data recording medium comprising at least one ofa character, a sign, a code, and an image formed by the method accordingto claim
 1. 5. An image forming apparatus configured to form an imageaccording to the method according to claim
 1. 6. The image formingapparatus according to claim 5, wherein a swelling level of the overlaidportion with reference to the non-overlaid portion is equal to or lessthan 10 μm.
 7. The image forming apparatus according to claim 5, whereinan area of at least one of the prevention image and the special-lightresponsive image in which the density of adherence of the image formingmaterial is small is broader than an area of the overlaid portion. 8.The image forming apparatus according to claim 5, wherein the density ofadherence of the image forming material in the overlaid portion isreduced toward an edge face of the one of the prevention image and thespecial-light responsive image.
 9. The image forming apparatus accordingto claim 5, wherein a printing rate at the overlaid portion is smallerthan a printing rate at the non-overlaid portion.
 10. The image formingapparatus according to claim 5, wherein density of adherence of theimage forming material in each one of the special-light responsive imageand the prevention image is reduced in the overlaid portion.
 11. Theimage forming apparatus according to claim 5, wherein the preventionimage and the special-light responsive image are overlaid on top of eachother only at an edge face of the prevention image or an area within aprescribed range from the edge face of the prevention image and an edgeface of the special-light responsive image or an area within aprescribed range from the edge face of the special-light responsiveimage.
 12. The image forming apparatus according to claim 11, whereindensity of adherence of the image forming material of the special-lightresponsive image in the overlaid portion is reduced toward an edge faceof the special-light responsive image, and wherein density of adherenceof the image forming material of the prevention image in the overlaidportion is reduced toward an edge face of the prevention image.
 13. Theimage forming apparatus according to claim 5, wherein a color differencebetween the special-light responsive image and the prevention imageunder visible light is equal to or smaller than 6.5.
 14. The imageforming apparatus according to claim 5, wherein a difference in glossvalue between the special-light responsive image and the preventionimage is equal to or smaller than 10%.
 15. The image forming apparatusaccording to claim 5, wherein the special light is infrared light. 16.An image forming apparatus configured to form an image according to themethod according to claim
 2. 17. The image forming apparatus accordingto claim 16, wherein a color difference between the special-lightresponsive image and the prevention image under visible light is equalto or smaller than 6.5.
 18. The image forming apparatus according toclaim 16, wherein a difference in gloss value between the special-lightresponsive image and the prevention image is equal to or smaller than10%.
 19. The image forming apparatus according to claim 16, wherein thespecial light is infrared light.
 20. An image forming apparatusconfigured to form an image according to the method according to claim3, wherein the special light is infrared light, and wherein density ofadherence of the image forming material of the special-light responsiveimage in the overlaid portion is reduced toward an edge face of thespecial-light responsive image.